It is necessary to have convenient access to the interior of luminaires for lamp replacement and service. A common arrangement favored for ceiling-mounted luminaires is to hinge the refractor to the lamp housing at one side so the refractor may be swung on the housing from closed to open position. Latch means are provided for locking the refractor in its closed position and for releasing it to give access to the interior. The refractor may vary from a simple flat light-transmitting plate or lens serving primarily as a window to keep out dirt and water, to an elaborately faceted clear bowl serving also to refract and redirect the light in particular directions.
Industrial luminaires of the foregoing type are frequently mounted at such heights that a ladder or elevated platform is used for servicing. For convenience and safety, a hinge and latch arrangement capable of being opened and closed by one hand, leaving to the workman his other hand free for supporting himself, is highly desirable.
The use of plastic instead of glass for the refractor has made relatively large low brightness luminaires practical for indoor use with low mounting heights. One can drill holes and drive screws into plastic but when doing so occasions stress concentrations, the plastic will develop cracks and deteriorate rapidly. For that reason the hinges and latches used with such plastic refractors have followed designs developed in the past for relatively heavy glass which avoided direct attachment of metal parts to glass. In one widely used design, the latching means comprise a metal clamp band encircling the entire refractor and a hinge and latches are attached to the metal band. This makes an elaborate and expensive design.